[Asterisk-Users] one extention, multiple phones

[Chris A. Icide]

On 05:11 PM 7/31/2004, Sean McKay wrote:
 > Also I'd like to say I believe this is possible with the CCM otherwise
 >how could an agent (operator) be able to monitor which extensions are in
 >use with the 7960 expansion device?

CCM doesn't use SIP to do this, it uses SCCP.  A proprietary cisco protocol.

The SIP protocol has been extended to include a subscribe and notify 
function, allowing a SIP UA to subscribe to a 'service' and be notified of 
changes in that service.  You could use this to at least be able to turn 
led's on and off, however, you would have to build some functionality into 
Asterisk to support a sip barging feature based upon picking up the handset 
attached to the notified line.  I'm not sure what the different sip phones 
that support subscribe/notify actually do when you hit that button when 
it's lit as well.  Obviously you would need some kind of signal from the 
phone to asterisk to request being connected to that media stream.  Would 
it be an INVITE?  How would it be formatted?  I'm sure all this is answered 
in the RFC that describes the subscribe/notify function, it's been way to 
long since I skimmed through it.

-Chris